Modem-Router Firewall

So I have been having endless problems for about 6 months with my Velop. I am in the UK, and have a Vodafone Connect Modem-Router that is ethernet into the Parent Node. In total I have 8 nodes over a 4 storey house - it is a terraced house, so I would say that there is a lot of wifi and noise from other networks nearby.

The main problem I had was with the mobile devices (iPads & iPhones) - when moving between nodes they would loose internet connection. It would resolve itself after about 10 minutes of not moving.

Having spoken to the Linksys helpline a number of times, I have disabled IPv6 and also manually set the channel to 6 - apparently with 8 nodes the Velop App Channel Finder will not work.

Yesterday, I switched off the firewall and DHCP on the Vodafone Connect Modem Router and I have had about 24 hours of stability - probably the longest I have ever acheived!! I am cautiously optimistic that my problem has been resolved... my basic, non-technical understanding is that it may have been a similiar issue to double NAT, where there were 2 DHCP's trying to resolve IP addresses.

One quesiton I had is on the firewall. I am assuming that as the firewall on the Velop is still enabled, I am alright. The Vodafone Modem Router is operating more like a modem only, with the firewall and DHCP disabled. I just wanted to confirm that this is alright and that the Velop Firewall will protect me enough.

Also - for those out there that are having problems, perhaps this might help you resolve... I am a little disappointed that it took so long to come to this solution - the setup on the Velop, I thought, specifically dealt with having modem-router for access to the internet didn't even consider this. Also, for those in the UK, I think that BT and Vodafone (not sure about other providers as these are the only 2 I have had since my velop), insist that you use their modem-routers for access to the fibre...